The several components of this study include definition of M- antigens among prevalent non-M-typable streptococci; defining relationship of M- serotypes to sites of infection; and a systematic investigation of type- specific antibody in streptococcal pyoderma. Immunity to streptococcal pharyngitis will also be studied and compared to pyoderma data. Evidence of possible "cross-protective" immunity following infection by similar or related serotypes will be determined. An experimental model (rabbit) for pyoderma will be used to explore mechanisms of immunity to pyoderma and to compare bactericidal immunity in immunized rabbits to that following skin infections. The effect of bactericidal antibody in preventing infections in rabbits will be determined. The search for new M-serotypes will begin with those streptococci agglutinated in the 8/25/Imp. 19 complex; these are important in both pyoderma and pharyngitis. Several pyoderma-nephritis strains share this complex. Relationships between M-types common to the 8/25/ Imp. 19 complex will be sought as will evidence for homologous and heterologous antibody in human sera. Subsequently collections including the 3/13/B3264 complex, common to pyoderma, will be examined in similar fashion. Sera from patients are by age, site of infection, chronological experiences with streptococcal infections and non- suppurative complications. The sera are systematically examined for the incidence and magnitude of type-specific antibody response by the indirect bactericidal method. Heterologous antibody is determined by examining sera with M-serotypes suspected to be related or similar to one-another. The incidence, frequency and significance of bactericidal antibody in streptococcal pyoderma will be compared with that in patients with pharyngitis, and findings related to earlier epidemiologic studies. Potential value of streptococcal vaccines for pyoderma should be clear following these studies.